Terry Reedy wrote: > On 1/24/2020 4:23 AM, Paul Moore wrote: > > On Fri, 24 Jan 2020 at 02:36, Guido van Rossum gu...@python.org wrote: > > I'm tempted to declare this > > implementation-defined behavior -- implicit calls to __eq__ and __ne__ > > may be skipped if both sides are the same object depending on the whim of > > the > > implementation. > > This sounds reasonable to me. It could be added to > > https://docs.python.org/3/reference/expressions.html#value-comparisons > > """ > > The default behavior for equality comparison (== and !=) is based on > > the identity of the objects. Hence, equality comparison of instances > > with the same identity results in equality, and equality comparison of > > instances with different identities results in inequality. A > > motivation for this default behavior is the desire that all objects > > should be reflexive (i.e. x is y implies x == y). > > """ > > We could add an extra clause here: """As an optimisation, when the > > implementation implicitly compares two values for equality (for > > example, in list comparison or list.count) it is allowed (but not > > required) to omit the equality check if the objects being compared are > > the same. This can result in different behaviour for objects with > > user-defined equality that is not reflexive - that is acceptable.""" > > This is an expanded version of what already exists further down, under > sequences. > " The built-in containers typically assume identical objects are equal > to themselves. That lets them bypass equality tests for identical > objects to improve performance and to maintain their internal invariants." > This was added last August, after careful consideration, by myself and > Raymond, as a beginner friendly replacement of 17 lines, that says what > users actually need to know.
For me this seems like an implementation-defined behaviour and the docs cover it already. _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/V4OZJSXWAYIRKK2RHLSAL2K7QU7T3DBJ/ Code of Conduct: http://python.org/psf/codeofconduct/
